This invention relates to module isolation devices for isolating the flow of gas from one module into one or more other modules that are joined together through one or more common headers. More specifically, this invention relates to isolation devices for Ion Transport Membrane (ITM) modules particularly designed for producing purified oxygen from an oxygen-containing gas (e.g., air) or for producing synthesis gas (often referred to herein as “syngas”).
The use of (ITM) modules for separating oxygen from an oxygen-containing gas, or for producing syngas is well known in the art. A representative patent disclosing ITM oxygen modules is Taylor et al. U.S. Pat. No. 5,681,373, assigned to the assignee of the present application. The Taylor et al. '373 patent is hereby fully incorporated herein by reference.
A representative patent application disclosing ITM syngas modules is Carolan et al. publication number US 20040186018, assigned to the assignee of the present application. The Carolan et al. '018 application is hereby fully incorporated herein by reference.
ITM oxygen and syngas modules typically are ceramic membranes that operate at high temperatures. These membranes operate with the process gas on one side of the membrane at a higher pressure than the process gas on the opposed side of the membrane. In common constructions a plurality of membrane modules are manifold together, both in series and in parallel, on a common header on the low-pressure gas side of the modules.
In an ITM oxygen module for separating oxygen from an oxygen-containing gas, the oxygen-containing gas is directed, under pressure, through passageways of the module to contact dense mixed conducting oxide layers of the multiple membranes making up the module. The driving force for separating the oxygen from the oxygen-containing gas is provided by creating a difference in oxygen partial pressure on opposite sides of the dense mixed conducting oxide layer of the various membranes, and the oxygen removed from the gas is then directed out of a product header, which generally is in communication with multiple ITM modules.
When the ITM modules are used for the production of synthesis gas the modules are generally heated to a temperature in the range of from 700 to 900° C., and the process temperature of the air inside the pipes that communicate with the ITM syngas modules are generally at the same operating temperature. In the production of synthesis gas a feed stock, which generally comprises a light hydrocarbon such as methane, natural gas, ethane, or other available light hydrocarbon mixtures known in the art, is introduced into passageways between the membranes of the ITM module. An oxygen-containing gas is introduced into the interior support layers of the various membranes of the module, wherein oxygen is permeated through the dense, mixed, outer conducting oxide layer of each of the membranes into engagement with the light hydrocarbon to form the synthesis gas.
If an individual membrane module fails, the high-pressure process gas will flow into the low-pressure process gas through the breach, or failure. In the case of an ITM oxygen module such failure results in a loss of purity of the permeate oxygen. In the case of an ITM syngas module, such failure results in syngas directly mixing with the source of air, which is a possible safety hazard. In addition, the failure may result in back pressuring the air feed to the other modules, may interfere with air flow or distribution and also may result in loss of the produced syngas.
From the above explanation it should be apparent that a need exists for a device or system that is capable of isolating an individual, failed module from the rest of the modules that are interconnected with the failed module by one or more common headers. Such an isolation device or system must be able to operate inside the process vessel, which is at an elevated temperature, and also must be reliable, and most preferably inexpensive in design. Shut off or isolation valves for use in conjunction with ITM modules are known in the art. These valves require an actuator to close them, and typically the actuators are pneumatic or electric solenoids triggered by an overpressure signal. These actuators are not designed for high temperature service in the inside of an ITM reactor vessel. In addition, lower cost devices would be beneficial. In this regard, a purely mechanical actuator is believed to have advantages over the use of pneumatic or electric solenoids from both a cost and reliability standpoint.
Use of a module isolation device or system will preserve product purity and also allows an ITM oxygen or syngas reactor to continue operating when individual modules fail, without compromising product purity, safety, or operability.
The problem addressed by the instant invention relates to the stopping of the flow of a gas resulting from a failed ITM module when the pressure of the gas exceeds a predetermined value. The device, including any actuator for it, must be able to operate at elevated temperatures, and must reliability permit the gas to flow through the device with an acceptable amount of restriction during normal operation.
Conventional technology using actuated valves responding to an overpressure signal from pressure transducers could accomplish the same function as the present invention, but with equipment of greatly increased complexity. Each module would require a separate pressure transducer to detect the presence of an increased pressure. Moreover, each module also would require an actuated valve. This may include the routing of pneumatic lines to each pneumatic actuator or electrical power to each electrical actuator. Hardware to perform the logic control of each actuator would also be required. For an ITM reactor, such as those employed in the preferred embodiments of this invention, the number and complexity of lines and equipment is significant.
U.S. Pat. No. 6,131,599 discloses a mechanically actuated pressure relief valve assembly controlled by a rupture disk. In the embodiment illustrated in FIG. 5 of the '599 patent, an excess pressure drop across the pressure responsive piston 212 pushes the actuating rod 216 through the rupture disk 204, thereby shutting off flow between the inlet 188 and the outlet 190. It should be noted that the rupture disk in the FIG. 5 embodiment of the '599 patent is not in flow communication with the process fluid. Stating this another way, the process fluid flows from the inlet to the outlet without in any way imposing the gas flow or pressure directly onto a surface of the rupture disk. In view of the fact that the device in the '599 patent works by a pressure difference across the piston, it is only sensitive to excessive flow through the device. In other words, it does not detect elevated pressure in the device unless that pressure is accompanied by an increased flow of gas. The pressure difference across the device is a function of the operating conditions of the device, such as the working fluid composition, the velocity of the fluid, the viscosity of the fluid and the density of the fluid. Thus, changing the operating conditions of the device changes the pressure difference across the device and hence changes the flow rate at which the rupture disk ruptures to shut off the gas flow. This is a limitation that should be avoided, and is not present in the devices of the present invention. As will be pointed out hereinafter, the isolation devices of the present invention actually shut off the flow gas at a given overpressure across the rupture disk, even in the absence of significant flow, such as when the inlet and outlet of the device are isolated.
A further deficiency in the device disclosed in FIG. 5 of the '599 patent is that it only is designed to operate with the valve seat and the actuator mechanism positioned on the outlet side of the housing. Such a device could not work on the air inlet of an ITM Syngas module. When an ITM Syngas module fails, the flow on the outlet leg will increase but the flow on the inlet leg will either stop or reverse due to the higher pressure in the module relative to the pressure of the feed air. A reversal of flow in the device disclosed in FIG. 5 of the '599 patent would force the valve 212 to stay open and would not apply any force to the rupture disk. The present invention can be employed with the valve seat located on either the inlet or outlet side of the normal flow direction, thereby making the design of the present invention more versatile.
Taylor U.S. Pat. No. 5,067,511 discloses a high-pressure fluid emergency shut-off valve. FIG. 3 of the '511 patent discloses a cross section of a typical valve in accordance with the teachings of that patent. Specifically, pressure at inlet 18 is transmitted through valve shaft 44 to an axial buckling pin 14. If the pressure is high enough, the pin 14 buckles to thereby allow the valve piston 47 to seat in valve seat 38, stopping fluid flow between inlet port 18 and outlet port 24. For pressure to be transmitted along valve shaft 44, sliding seals 48 are provided to maintain a pressure difference between the two ends of the shaft. The use of a buckling pin, as disclosed in the '511 patent, is materially different from the use of rupture disks in the devices of the present invention. Moreover, the required use of sliding seals 48 in the construction disclosed in the '511 patent makes such an arrangement unsuitable for use in high temperature applications, which are the preferred applications for the devices of the present invention.
Huff U.S. Pat. No. 4,240,458 discloses an excess pressure shut-off valve. FIGS. 2 and 3 of the '458 patent show a cross section of a typical valve in accordance with the teachings of that patent. Excess pressure in space 20 causes diaphragm 24, which is a bi-stable snap-acting disk, to snap into the other stable position. This moves valve shaft 64 upward in the figure to move O-ring 76 into sealing engagement with sealing surface 18, thereby shutting off flow between inlet 14 and outlet 16 of the device. A principal drawback of the design disclosed in the '458 patent is that the range of motion of the bi-stable snap-acting disk is small, being limited by the two stable positions of the disk. This results in a limited range of motion of the valve and hence only a limited opening of the valve into its fully opened position. In addition, any wear of the O-ring cannot be compensated for by additional axial movement of the valve shaft 64. The isolation valves employed in the module isolation devices of the present invention do not have these undesired, range-of-movement limitations.
Westman U.S. Pat. No. 5,810,057, assigned to the same assignee as the instant application, discloses a pressure vessel fill protective device consisting of a sliding piston 28, as shown in FIG. 1 of the patent. Port 58 is in flow communication with the head space of a vessel and also with a rupture disk 90. Port 56 is in flow communication with the head space of a vessel. In the event the head space of a vessel becomes over pressurized, the rupture disk 90 fails, depressurizing the space above the piston and thereby causing a force to be exerted on pin 40 to thereby cause that pin to fail. This results in the piston sliding upward to close off flow communication between ports 22 and 24. The system disclosed in the '057 patent requires the use of a piston-type valve, which requires sliding seals that may not be amenable to use at elevated temperature conditions. As pointed out earlier, the most desired uses of the module isolation devices of this invention are in connection with ITM modules that operate at elevated temperature conditions.
Brazier et al. U.S. Pat. No. 6,484,742 discloses a pressure-activated shut-off valve, as illustrated in FIG. 11. Excessively high pressure will be transmitted through the shaft 308, causing pin 216 to buckle. As pin 216 buckles, the valve plug 314 seats against the valve seat 316 to stop fluid flow. To generate a pressure difference sufficient to move the valve shaft 308, a good pressure seal is required around that shaft as it passes through valve body 302. It is highly desirable to design a system which does not require the use of any seals around the valve shaft, particularly for systems intended for use in high temperature applications. For operation at high elevated temperature, the valve and shaft disclosed in the '742 patent would need to be carefully constructed to prevent them from binding to each other. Alternatively, the seal area would have to be carefully insulated from any hot process fluid to prevent that area from becoming too hot. Also, unlike the present invention (as will become apparent from the discussion which follows) the pin that is required to buckle is not directly in the flow path through the cartridge assembly.